Advanced composite filtration media

ABSTRACT

This invention relates to advanced composite filtration media comprising (i) a functional filtration component and (ii) a matrix component, wherein said matrix component has a softening point temperature less than the softening point temperature of said functional filtration component, and wherein said functional filtration component is intimately bound to said matrix component; and methods for preparing and using same. More particularly, this invention pertains to advanced composite filter media and advanced composite filter media products comprised of a functional filtration component, such as a biogenic silica product (e.g., diatomite) or a natural glass product (e.g., expanded perlite) which bears a distinguishing porous and intricate structure suitable for filtration, which is thermally sintered to a matrix component, such as an engineering polymer (e.g., glasses, crystalline minerals, thermoplastics, and metals) that has a softening temperature below that of the functional filtration component. The advanced composite filtration media of the present invention offer unique properties such as increased permeability, low centrifuged wet density, low cristobalite content, and uniquely shaped particles (e.g., fibers).

TECHNICAL FIELD

This invention relates to advanced composite filtration media comprisinga functional filtration component and a matrix component, and methodsfor preparing and using same. More particularly, this invention pertainsto advanced composite filter media and advanced composite filter mediaproducts comprised of a functional filtration component, such as abiogenic silica product (e.g., diatomite) or a natural glass product(e.g., expanded perlite) which bears a distinguishing porous andintricate structure suitable for filtration, which is thermally sinteredto a matrix component, such as an engineering polymer (e.g., glasses,crystalline minerals, thermoplastics, and metals) that has a softeningtemperature below that of the functional filtration component.

DESCRIPTION OF THE RELATED ART

Throughout this application, various publications, patents, andpublished patent applications are referred to by an identifyingcitation; full citations for these documents may be found at the end ofthe specification immediately preceding the claims. The disclosures ofthe publications, patents, and published patent specificationsreferenced in this application are hereby incorporated by reference intothe present disclosure to more fully describe the state of the art towhich this invention pertains.

The present invention relates to advanced composite filtration mediacomprising (i) a functional filtration component and (ii) a matrixcomponent, wherein said matrix component has a softening pointtemperature less than the softening point temperature of said functionalfiltration component, and wherein said functional filtration componentis intimately bound to said matrix component. Unlike simple mixtures,which tend to segregate upon suspension (e.g., in fluids) or conveyanceor transport, the functional filtration components and matrix componentsof the advanced composite filtration media of the present invention areintimately bound, as achieved, for example, by thermal sintering.

The advanced composite filtration media of the present invention areuseful in many of the same applications as currently availablefiltration media, but offer one or more unique properties such as, forexample, increased permeability, low centrifuged wet density, lowcristobalite content, and/or uniquely shaped particles (e.g., fibers),as well as improved efficiency and/or economy, which are particularlyvaluable for filtration applications.

In the field of filtration, many methods of particle separation fromfluids employ diatomite products or natural glass products as filteraids. The intricate and porous structures unique to these siliceousmaterials is particularly effective for the physical entrapment ofparticles, for example, in filtration processes. These intricate andporous structures create networks of void spaces that result in buoyantfiltration media particles that have apparent densities similar to thoseof the fluids in which they are suspended. It is common practice toemploy filtration products when improving the clarity of fluids thatcontain suspended particles or particulate matter, or have turbidity.

Diatomite or natural glass products are often applied to a septum toimprove clarity and increase flow rate in filtration processes, in astep sometimes referred to as "precoating." Diatomite or natural glassproducts are also often added directly to a fluid as it is beingfiltered to reduce the loading of undesirable particulate at the septumwhile maintaining a designed liquid flow rate, in a step often referredto as "body feeding." Depending on the particular separation involved,diatomite or natural glass products may be used in precoating, bodyfeeding, or both. The working principles involved with porous mediafiltration have been developed over many years (Carman, 1937; Heertjes,1949, 1966; Ruth, 1949; Sperry, 1916; Tiller, 1953, 1962, 1964), andhave been recently reviewed in detail from both practical perspectives(Cain, 1984; Kiefer, 1991) as well as from their underlying theoreticalprinciples (Bear, 1988; Norden, 1994).

In certain circumstances, diatomite or natural glass products may alsoexhibit unique adsorptive properties during filtration that can greatlyenhance clarification or purification of a fluid. These adsorptiveproperties are highly specific, and depend upon weak forces forattraction of the adsorbed species to weak electrical charges at thesurface of diatomite, or upon the reactivity of silanol (i.e.,.tbd.Si--OH) functional groups that often occur at the diatomitesurface. For example, an ionized silanol group (i.e., .tbd.Si--O⁻) mayreact with a hydronium ion (i.e., H₃ O⁺) contributed by an acidicsubstance in solution, for example, citric acid (i.e., C₆ H₈ O₇),adsorbing the donated H⁺ at the surface in the process. In certaincircumstances, perlite products, especially those which are surfacetreated, may also exhibit unique properties during filtration that cangreatly enhance clarification or purification of a fluid (Ostreicher,1986).

In some filtration applications, different diatomite products may beblended together, or different natural glass products may be blendedtogether, to further modify or optimize the filtration process.Alternatively, diatomite products and natural glass products maysometimes be blended with each other, or with other substances. In somecases, these combinations may involve simple mixtures, for example, withcellulose, activated charcoal, clay, asbestos, or other materials. Inother cases, these combinations are more elaborate mixtures in whichdiatomite products or natural glass products are intimately blended withother ingredients to make sheets, pads, cartridges, or monolithic oraggregate media used as supports, substrates, or in the preparation ofcatalysts.

Still more elaborate modifications of any of these diatomite or naturalglass products are used for filtration or separation, involving, forexample surface treatment or the absorption of chemicals to diatomite ornatural glass products, mixtures, or their combinations.

The intricate and porous structure of silica unique to diatomite andnatural glass products also permits their commercial use to provideantiblock properties to polymers. Diatomite products are often used toalter the appearance or properties of paints, enamels, lacquers, andrelated coatings and finishes. Diatomite products are also used aschromatographic supports, and are especially suited to gas-liquidchromatographic methods. Recent reviews (Breese, 1994; Engh, 1994)provide particularly useful introductions to the properties and uses ofdiatomite. Many natural glass products, including, for example, expandedperlite, pumice, and expanded pumice, also possess unique fillerproperties. For example, expanded perlite products are often used asinsulating fillers, resin fillers, and in the manufacture of texturedcoatings.

The method of preparing monolithic or aggregate media is distinguishedfrom that of preparing advanced composite filtration media by the factthat components added for monolithic or aggregate media are added priorto thermal treatment as processing aids (e.g., clay) usually prior tothermal treatment to provide green strength to the unfired mixture(e.g., to enable the extruding, forming, molding, casting, or shaping ofgreen mixtures), rather than added as desired functional components ofan advanced composite filtration media. The addition of processing aidsdoes not otherwise favorably contribute to the filtrationcharacteristics of resulting monolithic or aggregate media products, butthese products are nevertheless useful for immobilization of proteins,enzymes, and microorganisms. The intent of thermal treatment (i.e.,firing) in the processing of technical ceramics from a physical mixtureof discrete particulate phases is to produce a dense homogeneous ceramicmaterial (Reynolds, 1979), unlike the sintered heterogeneous componentsof the advanced composite filtration media of the present invention.

SUMMARY OF THE INVENTION

One aspect of the present invention pertains to advanced compositefiltration media comprising (i) a functional filtration component and(ii) a matrix component, wherein said matrix component has a softeningpoint temperature less than the softening point temperature of saidfunctional filtration component, and wherein said functional filtrationcomponent is intimately bound to said matrix component.

In a preferred embodiment, the advanced composite filtration media has apermeability greater than the permeability of a simple mixture of saidfunctional filtration component and said matrix component (morepreferably greater by 5% or more), wherein the proportions of saidfunctional filtration component and said matrix component in said simplemixture are identical to those used in the preparation of said media.

In another preferred embodiment, the advanced composite filtration mediahas a median particle diameter greater than the weighted average of themedian particle diameter of said functional filtration component and themedian particle diameter of said matrix component (more preferablygreater by 5% or more), wherein the proportions of said functionalfiltration component and said matrix component are identical to thoseused in the preparation of said media.

In another preferred embodiment, the functional filtration component isselected from the group consisting of biogenic silica and natural glass;more preferably from the group consisting of diatomite, perlite, pumice,obsidian, pitchstone, and volcanic ash; still more preferably from thegroup consisting of diatomite, perlite, and volcanic ash; mostpreferably diatomite.

In another preferred embodiment, the matrix component is selected fromthe group consisting of glasses, crystalline minerals, thermoplastics,and metals. In another preferred embodiment the matrix component is anatural glass, more preferably selected from the group consisting ofperlite, pumice, obsidian, pitchstone, and volcanic ash, most preferablyperlite or fluxed perlite. In another preferred embodiment the matrixcomponent is a synthetic glass. In another preferred embodiment thematrix component is a fiber glass. In another preferred embodiment thematrix component is mineral wool or rock wool. In another preferredembodiment the matrix component is a thermoplastic or a thermosetpolymer with thermoplastic behavior. In another preferred embodiment thematrix component is a metal or a metal alloy.

In another preferred embodiment, the advanced composite filtration mediais further characterized by a cristobalite content of 1% or less byweight.

Another aspect of the present invention pertains to compositionscomprising an advanced composite filtration media, said media comprising(i) a functional filtration component and (ii) a matrix component,wherein said matrix component has a softening point temperature lessthan the softening point temperature of said functional filtrationcomponent, and wherein said functional filtration component isintimately bound to said matrix component. In a preferred embodiment,the composition is in the form of a powder. In another preferredembodiment, the composition is in the form of a sheet, pad, orcartridge. In another preferred embodiment, the composition is in theform of a monolithic support or an aggregate support. In anotherpreferred embodiment, the composition is in the form of a monolithicsubstrate or an aggregate substrate.

Yet another aspect of the present invention pertains to methods offiltration comprising the step of passing a fluid containing suspendedparticulates through a filter aid material supported on a septum,wherein said filter aid material comprises an advanced compositefiltration media, said media comprising (i) a functional filtrationcomponent and (ii) a matrix component, wherein said matrix component hasa softening point temperature less than the softening point temperatureof said functional filtration component, and wherein said functionalfiltration component is intimately bound to said matrix component.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A. Advanced Composite Filtration Media of the Present Invention

The advanced composite filtration media of the present inventioncomprise (i) a functional filtration component and (ii) a matrixcomponent, wherein said matrix component has a softening pointtemperature less than the softening point temperature of said functionalfiltration component, and wherein said functional filtration componentis intimately bound to said matrix component.

Many methods for the separation of particles from fluids employsiliceous media materials, such as diatomite, perlite, pumice, orvolcanic ash, as filtration media. The intricate porous structuresunique to these siliceous media materials are particularly effective forthe physical entrapment of particles in filtration processes; hence,they are useful as functional filtration components of the currentinvention. Dimensional stability and retention of mechanical propertiesthrough the course of thermal processing are characteristic features ofengineering polymers and certain other materials which makes them usefulas matrix components in the present invention. In the advanced compositefiltration media of the present invention, matrix components areintimately bound to functional filtration components, preferably bythermal sintering, and are not merely mixed or blended together. Unlikethe advanced composite filtration media of the present invention, suchsimple mixtures tend to segregate upon suspension (e.g., in fluids) orconveyance or transport. The term "simple mixture" is used herein in theconventional sense to mean mechanical mixtures or blends (e.g., whichhave not been subjected to thermal sintering).

The advanced composite filtration media of the present invention mayconveniently be considered to be an agglomerate of the functionalfiltration component and matrix component. The term "agglomeration" isused herein in the conventional sense to refer to any method or effectin which particles are assembled into a coherent mass. One example of anagglomeration method is thermal sintering, wherein particles are causedto become a coherent mass (i.e., are intimately bound), and therefore an"agglomerate", by heating without melting. Note that, in thermalsintering, agglomeration does not proceed to the point of forming ahomogeneous medium (e.g., a ceramic). Thus, in the advanced compositefiltration media of the present invention, functional filtrationcomponents and matrix components are agglomerated and intimately bound,but retain those physical and chemical properties which are deemed to bedesirable in the resulting product, and therefore enhance the overallproperties of the resulting product.

The term "softening point temperature" is used herein in theconventional sense to refer to the temperature at which a substancebegins to soften, and is usually associated with a decrease in hardnessand viscosity. For many engineering polymers, a softening point is oftenrecognized more specifically as the glass transition temperature,sometimes called the second-order transition temperature, which is thetemperature at which wriggling of polymer chains occurs as thetemperature is raised, i.e., the polymer changes from a rigid glassystate to a flexible solid. Polyether ketones, for example, have glasstransition temperatures of about 330° F. (i.e., 165° C.), whilesoda-lime glasses have softening points of about 1290° F. (i.e., 700°C.). While standard test methods, which usually employ thermomechanicalanalysis, have been developed (e.g., American Society for Testing andMaterials, 1995), the softening point can often be estimated visually inlaboratory studies without employing sophisticated quantitativedeterminations.

1. Functional Filtration Components

An especially preferred functional filtration component for use in thepresent invention is derived from biogenic silica (i.e., silicondioxide, SiO₂) which bears the distinguishing porous and intricatestructure of silica unique to diatomite. Currently, diatomite productsare used in a wide variety of applications, including, but not limitedto, separation, adsorption, support, and functional filler applications.

Diatomite products are obtained from diatomaceous earth (also known askieselguhr), which is a sediment enriched in the siliceous frustules,i.e., shells, of diatoms. Diatoms are a diverse array of microscopic,single-celled golden brown algae of the class Bacillariophyceae, inwhich the cytoplasm is contained within ornate siliceous frustules ofvaried and intricate structure. These frustules are sufficiently durableto retain much of their porous structure virtually intact through longperiods of geologic time when preserved in conditions that maintainchemical equilibrium. Currently, diatomite products may be manufacturedby a variety of methods and from numerous resources, offering diversityin physical and chemical characteristics. Recent reviews (Breese, 1994;Engh, 1994) provide particularly useful introductions to the propertiesand uses of diatomite.

In a typical conventional method of preparing commercial diatomiteproducts, crude ores of diatomaceous earth are crushed to a size thatcan be further reduced by milling, air classified, and dried in afurnace in air with subsequent air classification to achieve a desiredproduct permeability, thus forming a dried product, commonly referred toas "natural" diatomite.

In another conventional method, a natural product can be sintered in air(commonly called calcining) at temperatures typically ranging from 1800°to 2000° F. (i.e., 1000° to 1100° C.), followed by air classification.This method achieves more permeable products, but is usually accompaniedby partial conversion of amorphous silica (the natural phase of silicaof diatomaceous earth ores) to cristobalite, which is a tetragonal formof crystalline silica. Products made by this method typically havecristobalite contents ranging from 5 to 40% by weight.

In another conventional method, a dried product can also be furthersintered in air with the addition of a small quantity of flux (commonlycalled flux calcining) at temperatures typically ranging from 1800° to2100° F. (i.e., 1000° to 1150° C.), followed by air classification. Thismethod achieves still more permeable products, but usually with evengreater conversion of amorphous silica to cristobalite, which istypically present in the range of 20 to 75% by weight. The most commonlyused fluxes include soda ash (i.e., sodium carbonate, Na₂ CO₃) and rocksalt i.e., sodium chloride, NaCl), although many other fluxes,particularly salts of the alkali metals i.e., Group IA of the periodictable) are useful.

The high temperatures involved in the conventional methods of sinteringdiatomite products usually result in reduced surface area, enlargementof pores, increased wet density, and changes in impurity solubility, inaddition to the expected silica phase change from the amorphous state tocristobalite.

Other methods have been described in detail for processing diatomite andpreparing products made from diatomite. Much effort to improve low gradediatomaceous earths into higher grade ores has resulted in diatomiteproducts essentially equivalent in their overall quality to commercialproducts obtained from naturally better ores. Examples of such workincludes that of Norman and Ralston (1940), Bartuska and Kalina (1968a,1968b), Visman and Picard (1972), Tarhanic and Kortisova (1979), Xiao(1987), Li (1989), Liang (1990), Zhong et al. (1991), Brozek et al.(1992), Wang (1992), Cai et al. (1992), and Videnov et al. (1993).Several diatomite products that have been prepared with a singleproperty targeted for improvement, for example, reduced total iron orsoluble iron concentration, have been reported by Thomson and Barr(1907), Barr (1907), Vereinigte (1913, 1928), Koech (1927), Swallen(1950), Suzuki and Tomizawa (1971), Bradley and McAdam (1979), Nielsenand Vogelsang (1979), Heyse and Feigl (1980), and Mitsui et al. (1989).A diatomite product made by Baly (1939) had low organic matter, andCodolini (1953), Pesce (1955, 1959), Martin and Goodbue (1968), and Munn(1970) made diatomite products with relatively high brightness. Adiatomite product made by Enzinger (1901) reduced conventionalsolubility at that time. Diatomite products made by Bregar (1955),Gruder et al. (1958), and Nishamura (1958) were brighter, coupled with alower total iron concentration. A product made by Smith (1991a,b,c;1992a,b,c; 1993; 1994a,b) improved on the soluble multivalent cations ofa flux calcined diatomite product. Schuetz (1935), Filho and Mariz daVeiga (1980), Marcus and Creanga (1965), and Marcus (1967) also reportedmethods for making somewhat purer diatomite products. Dufour (1990,1993) describes a method for preparing diatomite products with lowcristobalite content.

None of the aforementioned products of diatomite, however, comprise (i)a functional filtration component and (ii) a matrix component, whereinsaid matrix component has a softening point temperature less than thesoftening point temperature of said functional filtration component, andwherein said functional filtration component is intimately bound to saidmatrix component.

Other functional filtration components of particular usefulness arederived from natural glasses which also bear distinguishing porous andintricate structures that are particularly effective for the physicalentrapment of particles in filtration processes. The term "naturalglass" is used herein in the conventional sense and refers to naturalglasses, commonly referred to as volcanic glasses, which are formed bythe rapid cooling of siliceous magma or lava. Several types of naturalglasses are known, including, for example, perlite, pumice, obsidian,and pitchstone. Prior to processing, perlite is generally gray to greenin color with abundant spherical cracks which cause it to break intosmall pearl-like masses. Pumice is a very lightweight glassy vesicularrock. Obsidian is generally dark in color with a vitreous luster and acharacteristic conchoidal fracture. Pitchstone has a waxy resinousluster and is frequently brown, green, or gray. Volcanic glasses such asperlite and pumice occur in massive deposits and find wide commercialuse. Volcanic ash, often referred to as tuff when in consolidated form,consists of small particles or fragments which are often in glassy form;as used herein, the term natural glass encompasses volcanic ash.

Most natural glasses are chemically equivalent to rhyolite. Naturalglasses which are chemically equivalent to trachyte, dacite, andesite,latite, and basalt are known but are less common. The term obsidian isgenerally applied to massive natural glasses that are rich in silica.Obsidian glasses may be classified into subcategories according to theirsilica content, with rhyolitic obsidians (containing typically about 73%SiO₂ by weight) as the most common (Berry, 1983).

Perlite is a hydrated natural glass containing typically about 72-75%SiO₂, 12-14% Al₂ O₃, 0.5-2% Fe₂ O₃, 3-5% Na₂ O, 4-5% K₂ O, 0.4-1.5% CaO(by weight), and small concentrations of other metallic elements.Perlite is distinguished from other natural glasses by a higher content(2-5% by weight) of chemically bonded water, the presence of a vitreous,pearly luster, and characteristic concentric or arcurate onion skin-like(i.e., perlitic) fractures.

Perlite products are often prepared by milling and thermal expansion,and possess unique physical properties such as high porosity, low bulkdensity, and chemical inertness. Expanded perlite has been used infiltration applications since about the late 1940's (Breese and Barker,1994). Conventional processing of perlite consists of comminution(crushing and grinding), air size classification, thermal expansion, andair size classification of the expanded material to meet thespecifications of the finished product. For example, perlite ore iscrushed, ground, and classified to a predetermined particle size range(e.g., passing 30 mesh), then classified material is heated in air at atemperature of 870°-1100° C. in an expansion furnace, where thesimultaneous softening of the glass and vaporization of contained waterleads to rapid expansion of glass particles to form a frothy glassmaterial with a bulk volume up to 20 times greater than that of theunexpanded ore. Often, the expanded perlite is then air classified andoptionally milled to meet the size specification of a desired product.The presence of chemically bonded water in other natural glasses (forexample, pumice, obsidian, and volcanic ash) often permits "thermalexpansion" in a manner analogous to that commonly used for perlite.

Pumice is a natural glass characterized by a mesoporous structure (e.g.,having pores or vesicles with a size up to about 1 mm). The highlyporous nature of pumice gives it a very low apparent density, in manycases allowing it to float on the surface of water. Most commercialpumice contains from about 60 to about 70% SiO₂ by weight. Pumice istypically processed by milling and classification (as described abovefor perlite), and products are primarily used as lightweight aggregatesand also as abrasives, absorbents, and fillers. Unexpanded pumice andthermally expanded pumice (prepared in a manner analogous to that usedfor perlite) may also be used as filter aids in some cases (Geitgey,1979), as can volcanic ash (Kansas Minerals, Inc., undated).

Modifications of methods and products for natural glasses have beenreported. For example, Houston (1959), Bradley (1979), Jung (1963),Morisaki (1976), Ruff and Nath (1982), and Shiuh (1982, 1985) describemethods for treatment that result in specialized natural glass products.

None of the aforementioned products of natural glass, however, comprise(i) a functional filtration component and (ii) a matrix component,wherein said matrix component has a softening point temperature lessthan the softening point temperature of said functional filtrationcomponent, and wherein said functional filtration component isintimately bound to said matrix component.

2. Matrix Components

Matrix components which are suitable for use in the preparation of theadvanced composite filtration media of the present invention arecharacterized by having a softening point temperature which is lowerthan the softening point temperature of the selected functionalfiltration component.

Examples of preferred matrix components include engineering polymers andrelated materials, which may be organic or inorganic polymers derivedfrom natural sources or produced synthetically. An excellent review ofengineering polymers has been prepared by Seymour (1990). Examples ofparticularly preferred matrix components include glasses, crystallineminerals, thermoplastics, and metals.

Glasses are vitreous amorphous polymers consisting of repeating siloxane(i.e., --(Si--O)--) units in the polymer chain. As described above, someglasses are naturally occurring, such as perlite, pumice, obsidian,pitchstone, and volcanic ash. Others, such as soda-lime glasses, areproduced synthetically. Soda-lime glass is made by melting batches ofraw materials containing the oxides of silicon (i.e., SiO₂), aluminum(i.e., Al₂ O₃), calcium (i.e., CaO), sodium (i.e., Na₂ O), and sometimespotassium (i.e., K₂ O), or lithium (i.e., Li₂ O) together in a furnace,and then allowing the melt to cool so as to produce the amorphousproduct. Glasses may be made in a wide variety of shapes, includingsheets or plates, cast shapes, or fibers. Methods of manufacturing theprincipal families of glasses have been reported (Scholes, 1974).Mineral wools, rock wools, and silicate cottons are generic names formanufactured fibers in which the fiber-forming substances may be slag,certain rocks, or glass (Kujawa, 1983).

Certain crystalline minerals, particularly silicate minerals andaluminosilicate minerals, and the rocks composed of mixtures of them,are useful matrix components of the present invention, because theyoften possess desirable thermoplastic characteristics (e.g., becausethey have chemistries related to those of many silicate glasses).Examples of such crystalline minerals include nepheline (a potassiumsodium aluminum silicate, i.e., (Na,K)AlSiO₄), albite (a sodium aluminumsilicate, i.e., NaAlSi₃ O₈), or calcium albite (a sodium calciumaluminum silicate, i.e., (Na,Ca)(Si,Al)₄ O₈).

Thermoplastic materials are those which soften under the action of heatand harden again to their original characteristics on cooling, that is,the heating-cooling cycle is fully reversible. By conventionaldefinition, thermoplastics are straight and branched linear chainorganic polymers with a molecular bond. Examples of well-knownthermoplastics include products of acrylonitrile butadiene styrene(ABS), styrene acrylonitrile (SAN), acrylate styrene acrylonitrile(ASA), methacrylate butadiene styrene (MBS). Also included are polymersof formaldehyde, known as acetals; polymers of methyl methacrylate,known as acrylic plastics; polymers of monomeric styrene, known aspolystyrenes; polymers of fluorinated monomers, known as fluorocarbons;polymers of amide chains, known as nylons; polymers of paraffins andolefins, known as polyethylenes, polypropylenes, and polyolefins;polymers composed of repeating bisphenol and carbonate groups, known aspolycarbonates; polymers of terephthalates, known as polyesters;polymers of bisphenol and dicarboxylic acids, known as polyarylates; andpolymers of vinyl chlorides, known as polyvinyl chlorides (PVC). Highperformance thermoplastics have extraordinary properties, for example,polyphenylene sulfide (PPS), which has exceptionally high strength andrigidity; polyether ketone (PEK), polyether ether ketone (PEEK),polyamide imide (PAI), which have very high strength and rigidity, aswell as exceptional heat resistance; and polyetherimide (PEI), which hasinherent flame resistance. Unusual thermoplastics include ionomers,i.e., copolymers of ethylene and methacrylic acid that have ionic ratherthan covalent crosslinking which results in behavior resembling that ofthermoset plastics in their operating range; polyvinylcarbazole, whichhas unique electrical properties; and polymers of isobutylene, known aspolyisobutylenes, which are viscous at room temperature.

Thermoset plastics are synthetic resins that are permanently changedupon thermal curing, that is, they solidify into an infusible state sothat they do not soften and become plastic again upon subsequentheating. However, certain thermoset plastics may exhibit thermoplasticbehavior over a limited portion of their useful application ranges, andare similarly useful as matrix components of the present invention. Sometypes of thermoset plastics, especially certain polyesters and epoxides,are capable of cold curing at room temperature. Thermoset plasticsinclude alkyds, phenolics, epoxides, aminos (including urea-formaldehydeand melamine-formaldehyde), polyimides, and some silicon plastics.

The properties and applications of thermoplastics and thermoset plasticshave been described in detail (Elsevier, 1992; Rubin, 1990).

Certain metals and metal alloys are useful matrix components,particularly low melting temperature metals and alloys, in that theypossess thermoplastic characteristics useful in the present invention.Examples of suitable metals are tin (i.e., Sn), zinc (i.e., Zn) and lead(i.e., Pb). Examples of suitable metal alloys are solders such astin-lead solder (i.e., Sn--Pb), tin-zinc solder (i.e., Sn--Zn), andzinc-lead solder (i.e., Zn--Pb).

Other materials with similar thermoplastic characteristics and which arecharacterized by a softening point temperature that is lower than thesoftening point temperature of the selected functional filtrationcomponent may also be useful as matrix components in the presentinvention.

B. Methods for Characterizing the Advanced Composite Filtration Media ofthe Present Invention

The advanced composite filtration media of the present invention possessunique properties, as they are comprised of both a functional filtrationcomponent as well as a matrix component. These media retain theintricate and porous structure that is characteristic of the functionalfiltration component (which is essential in many applications for theadvanced composite filtration media product to be effective) asevidenced by the media having suitable permeability in ranges useful tofiltration. The advanced composite filtration media, however, aremodified by the presence of a matrix component. These modifications areillustrated by unique properties such as increased permeability, lowcentrifuged wet density, low cristobalite content, and/or changes inmicrostructural characteristics.

Important properties of the advanced composite filtration media of thepresent invention, and suitable methods for their determination, aredescribed in detail below.

1. Permeability

Functional filtration products are usually processed to provide a rangeof filtration rates, which are closely related to their permeability, P.Permeability is often reported in units of darcies, commonly abbreviated"Da,"; 1 darcy corresponds to the permeability through a filter media 1cm thick which allows 1 cm³ of fluid with a viscosity of 1 centipoise topass through an area of 1 cm² in 1 sec under a pressure differential of1 atm (i.e., 101.325 kPa). Permeability is readily determined (EuropeanBrewery Convention, 1987) using a specially constructed device designedto form a filter cake on a septum from a suspension of filtration mediain water, and then measuring the time required for a specified volume ofwater to flow through a measured thickness of filter cake of knowncross-sectional area. The principles have been previously derived forporous media from Darcy's law (Bear, 1972), and so an array ofalternative devices and methods are in existence that correlate wellwith permeability. Filtration media, such as diatomite and natural glassproducts that are currently commercially available (and which are alsosuitable for use as functional filtration components of the presentinvention) span a wide range of permeability, from less than 0.05 Da toover 30 Da. The selection of the filtration permeability for a specificfiltration process depends on the flow rate and degree of fluidclarification desired for the particular application.

The advanced composite filtration media of the present invention offer aspectrum of permeabilities comparable to the range offered by theircommercial functional filtration components.

Evidence of agglomeration and thus the formation of the advancedcomposite filtration media (i.e., wherein the functional filtrationcomponent and the matrix component are intimately bound) may generallybe provided by observing a larger permeability for the advancedcomposite filtration media (after thermal sintering and unmilled, i.e.,without further attrition or classification) than for the simple mixtureof its components (i.e., prior to thermal sintering).

For example, if a simple mixture of a functional filtration componentand a matrix component (having permeabilities of 0.06 Da and 0.29 Da,respectively) has a permeability, P(a+b), of 0.07 Da, and the advancedcomposite filtration media prepared from this simple mixture has apermeability, P(c), of 0.20 Da, then the increase in permeability isevidence of agglomeration. Preferably, P(c) is greater than P(a+b) by 5%or more, more preferably 10% or more, yet more preferably 20% or more.

2. Wet Density

An indicator of the degree to which the advanced composite filtrationmedia product of the current invention retains the porous and intricatestructure of its functional filtration media component may be obtainedby measuring its centrifuged wet density, which represents its usefulpacked density in filtration, since the magnitude of the density islimited by the packing arrangement that can be achieved. Wet density iscritical because it reflects the void volume available to entrainparticulate matter in a filtration process; it is one of the mostimportant criteria to determine the filtration efficiency. Filtrationproducts with lower wet densities have greater void volumes, and thusgreater filtration efficiency.

The preferred method for determining the packed density of the advancedcomposite filtration media products of the present invention is bymeasurement of the centrifuged wet density. A sample of known weightbetween 0.50 and 1.00 g is placed in a calibrated 14 mL centrifuge tube,to which deionized water is added to make up a volume of approximately10 mL. The mixture is shaken thoroughly until all of the sample iswetted and there is no dry powder remaining. Additional deionized wateris added around the top of the centrifuge tube to rinse down any mixtureadhering to the side of the tube from shaking. The tube is centrifugedfor 30 min at 1800 rpm. Following centrifugation, the tube is carefullyremoved so as not to disturb the solids, and the level (i.e., volume) ofthe settled matter is measured to the nearest half of a 0.05 mLgraduation on the tube. The centrifuged wet density of the known weightof powder is readily calculated by dividing the dry sample weight (e.g.,dried at 110° C. in air to constant weight) by the measured volume.

Typical wet densities for common filtration media range from as low asabout 12 pounds per cubic foot (i.e., 0.19 g/cm³) to as high as about 30pounds per cubic foot (i.e., 0.48 g/cm³). The advanced compositefiltration media of the present invention offer a spectrum of wetdensities comparable to the range offered by their commercial functionalfiltration components.

3. Particle Size

An important characteristic of the advanced composite filtration mediaof the present invention relates to agglomeration of the componentparticles, preferably through thermal sintering. One method forquantifying the degree of agglomeration involves determining thedifference in particle size distribution between the components (i.e.,before agglomeration) and the resulting advanced composite filtrationmedia.

The preferred method for determining particle size distribution employslaser diffraction. The preferred instrument for determining the particlesize distribution of the advanced composite filtration media, or itscomponents, is a Leeds & Northrup Microtrac Model X-100. The instrumentis fully automated, and the results are obtained using a volumedistribution formatted in geometric progression of 100 channels, runningfor 30 seconds with the filter on. The distribution is characterizedusing an algorithm to interpret data from the diffraction pattern whichassumes the particles have spherical shape characterized by a diameter,D. A median particle diameter is identified by the instrument as D₅₀,that is, 50% of the total particle volume is accounted for by particleshaving a diameter equal to or less than this value.

Evidence of agglomeration and thus the formation of the advancedcomposite filtration media (i.e., wherein the functional filtrationcomponent and the matrix component are intimately bound) may be providedby calculating the weighted average of the median particle diameter ofthe simple mixture of the functional filtration component and the matrixcomponent (i.e., prior to thermal sintering) and the median particlediameter of the advanced composite filtration media prepared using thatmixture (after thermal sintering and unmilled, i.e., without furtherattrition or classification).

For example, agglomeration has occurred when the weighted average, D₅₀(a+b), of the median particle diameter of the functional filtrationcomponent, D₅₀ (a), and the median particle diameter of the matrixcomponent, D₅₀ (b), is less than the median particle diameter of theadvanced composite filtration media, D₅₀ (c). For example, if D₅₀ (a) isequal to 16.7 μm and comprises 70% by weight of the advanced compositefiltration media, and if D₅₀ (b) is equal to 17.3 μm and comprises 30%by weight of the advanced composite filtration media, then, ##EQU1##

If the actual measured median particle diameter of the advancedcomposite filtration media, D₅₀ (c), is equal to 17.1 μm, thenagglomeration has occurred, since D₅₀ (a+b) is less than D₅₀ (c).Preferably, D₅₀ (c) is greater than D₅₀ (a+b) by 1% or more, morepreferably 5% or more, still more preferably 10% or more, yet morepreferably 20% or more.

The application of the particle size method is most appropriate whenparticles of the functional filtration component, the matrix component,and the advanced composite filtration media all have approximately equaldensities and approximate the spherical shape of particles assumed bythe algorithm. For matrix components that are fibrous in nature, themore general permeability method is preferred.

4. Cristobalite Concentration

Some advanced composite filtration media are unique in that thecristobalite content is very low compared with commercial diatomiteproducts of comparable permeability. The preferred method fordetermining cristobalite content is by quantitative x-ray diffractionaccording to the principles outlined by Klug and Alexander (1974). Asample is milled in a mortar and pestle to a fine powder, thenback-loaded into an aluminum holder. The sample and its holder areplaced into the beam path of an x-ray diffraction system and exposed tocollimated x-rays using an accelerating voltage of 40 kV and a currentof 20 mA focused on a copper target. Diffraction data are acquired bystep-scanning over the angular region representing the interplanarspacing within the crystalline lattice structure of cristobalite thatyields the greatest diffracted intensity. This area lies between 21 to23 2θ°, with data collected in 0.05 2θ° steps, counted for 20 secondsper step. The net integrated peak intensity is compared with those ofstandards of cristobalite prepared by the standard additions method inamorphous silica to determine the weight percent of the cristobalitephase in a sample.

Preferably, the cristobalite content of the advanced compositefiltration media of the present invention is less than 1% (usually fromabout 1% to as low as the detection limit), more preferably less than1.1% (usually from about 1.1% to as low as the detection limit), stillmore preferably less than 1.5% (usually from about 1.5% to as low as thedetection limit), yet more preferably less than 2% (usually from about2% to as low as the detection limit), still more preferably less than 3%(usually from about 3% to as low as the detection limit), yet morepreferably less than 5% (usually from about 5% to as low as thedetection limit), still more preferably less than 10% (usually fromabout 10% to as low as the detection limit).

5. Microstructural Characteristics

The microstructural characteristics of the advanced composite filtrationmedia are often different from those of the functional filtrationcomponent and matrix component prior to thermal sintering. Microscopicfeatures of the advanced composite filtration media of the presentinvention are readily observed by preparing a suspension in a liquid ofan appropriate refractive index (e.g., water) on glass slides andobserving them under an optical microscope at magnifications of 200× and400×. At these magnifications, the intricate and porous structures foundin functional filtration components and the microscopic characteristicsof the matrix components are clearly visible.

C. Methods for Preparing the Advanced Composite Filtration Media of thePresent Invention

A convenient method of preparing advanced composite filtration media ofthe present invention is by blending a functional filtration componentwith a matrix component, followed by application of heat to causesintering and agglomeration to occur (i.e., thermal sintering).

The functional filtration component and matrix component may be mixed inany proportion, and the proportions employed are determined by theselected functional filtration component and matrix component and by theadvanced composite filtration media sought. For example, at thematrix-poor end of the spectrum, the matrix component may typicallycomprise as little as 0.5 to 5% by weight (i.e., of the simple mixturecomprising the functional filtration component and the matrix component,prior to thermal sintering), whereas, at the matrix-rich end of thespectrum, the matrix component may typically comprise as much as 70 to90% by weight (i.e., of the simple mixture comprising the functionalfiltration component and the matrix component, prior to thermalsintering).

Blending of the functional filtration component with a matrix component,prior to heat treatment, may be readily accomplished using, for example,a mechanical mixer, for a suitable length of time to allow thecomponents to become thoroughly mixed.

Heat may be applied using, for example, a conventional oven, microwaveoven, infrared oven, muffle furnace, kiln, or a thermal reactor, inambient atmospheres such as, for example, air, or artificial atmospheressuch as, for example, nitrogen (i.e., N₂) or oxygen (i.e., O₂) attemperatures typically ranging from 100° to 2500° F. (i.e., 40° to 1400°C.) and at pressures ranging from 0.1 to 50 atm (i.e., 1 to 5000 kPa).Heat treatment parameters, such as temperature and duration, aredetermined by the selected functional filtration component and matrixcomponent and by the advanced composite filtration media sought. Forexample, durations may range from about 1 ms (e.g., in fluidized bedreactors) to about 10 hours (e.g., in conventional furnaces). Suitabletemperatures (i.e., to achieve thermal sintering) are typically at aboutthe softening point temperature of the matrix component but below itsmelting point (i.e., not in the molten state).

Further modifications of the advanced composite filtration media of thepresent invention are also possible. For example, the advanced compositefiltration media may be further processed to enhance one or moreparticular properties (for example, solubility or surfacecharacteristics), or to yield a new product with a specialized use.Examples of such further modifications include, for example, acidwashing, surface treatment, and organic derivatization.

1. Acid Washing

Another class of products may be prepared from the advanced compositefiltration media described above by washing with an acidic substance,followed by rinsing with deionized water to remove residual acid, andsubsequent drying. Acid washing of the advanced composite filtrationmedia is beneficial in reducing the concentration of solublecontaminants, e.g., iron or aluminum. Suitable acids include mineralacids, for example, sulfuric acid (i.e., H₂ SO₄), hydrochloric acid(i.e., HCl), phosphoric acid (i.e., H₃ PO₄), or nitric acid (i.e.,HNO₃), as well as organic acids, for example, citric acid (i.e., C₆ H₈O₇) or acetic acid (i.e., CH₃ COOH).

2. Surface Treatment

Another class of products can be prepared by treatment of the surface ofadvanced composite filtration media products described above, forexample, by silanization, thereby modifying the product's surface suchthat it is rendered either more hydrophobic or more hydrophilic.

For example, the advanced composite filtration media may be placed in aplastic vessel, and a small quantity of dimethyldichlorosilane (i.e.,SiCl₂ (CH₃)₂) or hexamethyldisilazane (i.e., (CH₃)₃ Si--NH--Si(CH₃)₃) isadded to the vessel. Reaction is allowed to take place at the surface inthe vapor phase over a 24 hr period, resulting in more hydrophobicproducts. Such products have application in compositions used inchromatography, and also when used in conjunction with other hydrophobicmaterials for improved mechanical performance, for example, inapplications involving hydrocarbons and oils.

Similarly, the advanced composite filtration media can be reacted, forexample, by suspending it in a solution containing 10% (w/v)aminopropyltriethoxysilane (i.e., C₉ H₂₃ NO₃ Si) in water, refluxing at700° C. for 3 hr, filtering the mixture, and drying the remaining solidsto obtain more hydrophilic products. Such products have applications incompositions used in chromatography, when used in conjunction withaqueous systems for improved mechanical performance, and to permitfurther derivatization of the product, having converted terminalhydroxyl (i.e., --OH) functional groups of the advanced compositefiltration media product surface to aminopropyl groups (i.e., --(CH₂)₃NH₂).

3. Organic Derivatization

The hydrophilic (e.g., silanized) modified advanced composite filtrationmedia products can further be reacted to bind organic compounds, forexample, a protein. The advanced composite filtration media may therebyserves as a support for the immobilization of organic compounds. Somodified, the product has utility in applications such as affinitychromatography and biochemical purification.

A number of other reactions pertaining to derivatization of siliceousmedia products have been previously described (Hermanson, 1992).However, derivatization of the advanced composite filtration media ofthe present invention yields modified products with substantiallysuperior efficacy as a result of the incorporation of a matrixcomponent.

D. Methods of Using the Advanced Composite Filtration Media of thePresent Invention

The advanced composite filtration media products of the presentinvention, and their further modifications, are useful in theprocessing, treatment, or formulation of other materials.

In filtration applications, the advanced composite filtration media ofthe present invention, and their further modifications, may be appliedto a septum to improve clarity and increase flow rate in filtrationprocesses (e.g., precoating), or added directly to a fluid as it isbeing filtered to reduce the loading of undesirable particulate at theseptum (e.g., body feeding).

The advanced composite filtration media of the present invention may beused in conjunction with other media (i.e., to form a filter aidcomposition) for filtration applications. For example, mixtures of theadvanced composite filtration media with, for example, diatomite,perlite, natural glass, cellulose, activated charcoal, clay, or othermaterials are useful filter aid compositions. In other more elaboratecombinations, advanced composite filtration media are blended with otheringredients to make sheets, pads, and cartridges.

The appropriate selection of which composition or modification of anadvanced composite filtration media product is preferred is determinedby the specific application. For example, in a filtration process thatdemands exceptional clarity but tolerates slower flow rate, an advancedcomposite filtration media product of low permeability is preferred,whereas in a filtration process that demands high flow rate but does notrequire exceptional clarity, an advanced composite filtration mediaproduct of high permeability is preferred. Similar reasoning applies touse of the advanced composite filtration media products when used inconjunction with other materials, or when preparing mixtures containingthe product. The quantity of product which is used is similarlydetermined by the specific process to which it is applied.

The advanced composite filtration media of the present invention arealso useful in non-filtration applications, such as functional fillers,for example. In paints and coatings, or in papers or polymers, thisfeature is usually accomplished by direct addition into the formulationat a concentration needed for the desired effect. Both the flattingproperty of the products in paints and coatings as well as the antiblockproperty of the products in polymers are derived from the uniquesurfaces provided by the advanced composite filtration media.

The silanized hydrophobic or hydrophilic products are desirable whenthese properties further improve the filtration or functional fillerperformance, owing to their greater compatibility with other materialsor ingredients in a specific application. The alteration of surfacecharacteristics through silanization is especially critical tochromatographic applications, as these characteristics stronglyinfluence the effectiveness of chromatographic separations for specificsystems. For example, hydrophobic surfaces on a chromatographic supportreduce surface activity of the support and reduce tailing to aconsiderable degree when used for the analytical determination ofpesticides.

The products are also desirable for further organic derivatizations,such as the coupling of a protein to an aminosilanized support. Forexample, protein A, a polypeptide derived from a bacterial source, canbe coupled to an aminosilanized support prepared from the advancedcomposite filtration media.

In other applications, the advanced composite filtration media may beblended with other ingredients to make monolithic or aggregate mediauseful as supports (e.g., for microbe immobilization), substrates (e.g.,for enzyme immobilization), or in the preparation of catalysts.

Many other modifications and variations of the invention as hereinbeforeset forth can be made without departing from the spirit and scopethereof and therefore only such limitations should be imposed as areindicated by the appended claims.

E. EXAMPLES

Several advanced composite filtration media of the present invention,and methods for preparing them, are described in the following examples,which are offered by way of illustration and not by way of limitation.

Example 1

Diatomite (70%)+Perlite (30%)

In this example, an advanced composite filtration media was formulatedby combining 70% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), and30% by weight with a matrix component, HARBORLITE 200, a milled expandedperlite with a permeability of 0.29 Da, a wet density of 14.0 pounds percubic foot (i.e., 0.224 g/cm³), and a median particle diameter, D₅₀ (b),of 17.3 μm (Harborlite Corporation, Vicksburg, Mich.). The mixture wassintered in air in a muffle furnace at 1700° F. (i.e., 930° C.) for 45min, then removed from the furnace and allowed to cool to roomtemperature, forming the advanced composite filtration media.

The advanced composite filtration media of this example had apermeability of 0.20 Da, a wet density of 14.5 pounds per cubic foot(i.e., 0.232 g/cm³), a median particle diameter, D₅₀ (c), of 17.1 μm,and a cristobalite content of 0.1%.

By comparison, a simple mixture of the components of this example has apermeability of 0.07 Da, a wet density of 17.1 pounds per cubic foot(i.e., 0.274 g/cm³), and a median particle diameter of 17.0 μm.Furthermore, commercial diatomite products of permeability comparable tothat of the advanced composite filtration media of this example have atypical cristobalite content of about 20% and a wet density of about 19pounds per cubic foot (i.e., 0.30 g/cm³). Thus, the advanced compositefiltration media of this example offers highly unique properties notoffered by the individual media components or by commercial diatomiteproducts of comparable permeability.

Example 2

Diatomite (90%)+Perlite (10%)+Acid Flux

In this example, an advanced composite filtration media was formulatedby combining 90% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), 10%by weight with a matrix component, HARBORLITE 200, a milled expandedperlite with a permeability of 0.29 Da, a wet density of 14.0 pounds percubic foot (i.e., 0.224 g/cm³), and a median particle diameter, D₅₀ (b),of 17.3 μm (Harborlite Corporation, Vicksburg, Mich.), the mixture thencombined with 2% boric acid (i.e., H₃ BO₃) as an acid flux to reduce thesoftening temperature of perlite. The mixture was sintered in air in amuffle furnace at 1700° F. (i.e., 930° C.) for 30 min, then removed fromthe furnace and allowed to cool to room temperature, forming theadvanced composite filtration media.

The advanced composite filtration media of this example had apermeability of 0.69 Da, a wet density of 13.0 pounds per cubic foot(i.e., 0.208 g/cm³), a median particle diameter, D₅₀ (c), of 20.3 μm,and a cristobalite content of 0.5%.

By comparison, a simple mixture of the components of this example has apermeability of 0.06 Da, and a wet density of 17.3 pounds per cubic foot(i.e., 0.277 g/cm³). Furthermore, commercial diatomite products ofpermeability comparable to that of the advanced composite filtrationmedia of this example have a typical cristobalite content of about 40%and a wet density of about 19 pounds per cubic foot (i.e., 0.30 g/cm³).Thus, the advanced composite filtration media of this example offersunique properties not offered by the individual media components or bycommercial diatomite products of comparable permeability.

Example 3

Diatomite (50%)+Perlite (50%)+Acid Flux

In this example, an advanced composite filtration media was formulatedby combining 50% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), 50%by weight with a matrix component, HARBORLITE 700, a milled expandedperlite with a permeability of 0.73 Da, a wet density of 14.5 pounds percubic foot (i.e., 0.232 g/cm³), and a median particle diameter, D₅₀ (b),of 30.2 μm (Harborlite Corporation, Vicksburg, Mich.), the mixture thencombined with 5% boric acid (i.e., H₃ BO₃) as an acid flux to reduce thesoftening temperature of perlite. The mixture was sintered in air in amuffle furnace at 1700° F. (i.e., 930° C.) for 30 min, then removed fromthe furnace and allowed to cool to room temperature, forming theadvanced composite filtration media.

The advanced composite filtration media of this example had apermeability of 1.9 Da, a wet density of 11.3 pounds per cubic foot(i.e., 0.181 g/cm³), a median particle diameter, D₅₀ (c), of 33.5 μm,and a cristobalite content of 0.1%.

By comparison, a simple mixture of the components of this example has apermeability of 0.10 Da, a wet density of 15.8 pounds per cubic foot(i.e., 0.253 g/cm³), and a median particle diameter of 26.4 μm.Furthermore, commercial diatomite products of a permeability comparableto that of the advanced composite filtration media of this example havea typical cristobalite content of about 50% and a wet density of about19 pounds per cubic foot (i.e., 0.30 g/cm³). Thus, the advancedcomposite filtration media of this example offers unique properties notoffered by the individual media components or by commercial diatomiteproducts of comparable permeability.

Example 4

Diatomite (70%)+Basic Fluxed Perlite (30%)

In this example, an advanced composite filtration media was formulatedby combining 70% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), 30%by weight with a matrix component, HARBORLITE 700, a milled expandedperlite with a permeability of 0.73 Da, a wet density of 14.5 pounds percubic foot (i.e., 0.232 g/cm³), and a median particle diameter, D₅₀ (b),of 30.2 μm (Harborlite Corporation, Vicksburg, Mich.), the lattercomponent of which was preheated for 10 min at 1700° F. (i.e., 930° C.)with 2% soda ash (i.e., sodium carbonate, Na₂ CO₃) as a basic flux toreduce the softening temperature of perlite. The mixture was thensintered in air in a muffle furnace at 1700° F. (i.e., 930° C.) for 30min, and removed from the furnace and allowed to cool to roomtemperature, forming the advanced composite filtration media.

The advanced composite filtration media of this example had apermeability of 0.38 Da, a wet density of 14.5 pounds per cubic foot(i.e., 0.232 g/cm³), a median particle diameter, D₅₀ (c), of 24.8 μm,and a cristobalite content of 0.9%.

By comparison, a simple mixture of the components of this example has apermeability of 0.07 Da, a wet density of 16.4 pounds per cubic foot(i.e., 0.263 g/cm³), and a median particle diameter of 24.2 μm.Furthermore, commercial diatomite products of permeability comparable tothat of the advanced composite filtration media of this example have atypical cristobalite content of about 30% and a wet density of about 19pounds per cubic foot (i.e., 0.30 g/cm³). Thus, the advanced compositefiltration media of this example offers unique properties not offered bythe individual media components or by commercial diatomite products ofcomparable permeability.

Example 5

Diatomite (50%)+Polyether Ketone (50%)

In this example, an advanced composite filtration media was formulatedby combining 50% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), and50% by weight with a matrix component, KADEL E1000C, a polyether ketone(Amoco Performance Products, Alpharetta, Ga.). The mixture was sinteredin air in a muffle furnace at 400° F. (i.e., 200° C.) for 30 min, thenremoved from the furnace and allowed to cool to room temperature,forming the advanced composite filtration media.

The advanced composite filtration media of this example had apermeability of 0.13 Da, a wet density of 19.8 pounds per cubic foot(0.317 g/cm³), a median particle diameter, D₅₀ (c), of 61.1 μm, and acristobalite content of less than 0.1%.

By comparison, a simple mixture of the components of this example has apermeability of 0.07 Da, a wet density of 23.1 pounds per cubic foot(i.e., 0.370 g/cm³), and a median particle diameter of 31.3 μm. Becauseof the hydrophobic characteristics of polyether ketone alone, comparablemeasurements of permeability, wet density, and median particle diameterare not possible by the methods otherwise preferred. The product isunique in that the thermoplastic partly penetrates the pores of thefunctional filtration component, yet also results in agglomeration.Thus, the advanced composite filtration media of this example offershighly unique properties not offered by the individual media components.

Example 6

Diatomite (85%)+Rock Wool (15%)

In this example, an advanced composite filtration media was formulatedby combining 85% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), and15% by weight with a matrix component, ground rock wool (USG Interiors,Inc., Chicago, Ill.) having brown, isotropic fibers 5 to 20 μm indiameter and 50 to 300 μm in length, with a wet density of 69.3 poundsper cubic foot (i.e., 1.11 g/cm³). The mixture was sintered in air in amuffle furnace at 1700° F. (i.e., 930° C.) for 30 min, then removed fromthe furnace and allowed to cool to room temperature, forming theadvanced composite filtration media.

The advanced composite filtration media of this example had apermeability of 0.25 Da, a wet density of 17.8 pounds per cubic foot(i.e., 0.285 g/cm³), and less than 0.1% cristobalite.

By comparison, a simple mixture of the two components of this examplehas a permeability of 0.06 Da, a wet density of 19.5 pounds per cubicfoot (i.e., 0.313 g/cm³), and a median particle diameter of 17.6 μm. Theproduct is unique in that the microstructural features of the rock woolare retained. Thus, the advanced composite filtration media of thisexample offers highly unique properties not offered by the individualmedia components.

Example 7

Diatomite (95%)+Fiber Glass (5%)

In this example, an advanced composite filtration media was formulatedby combining 95% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), and5% by weight with a matrix component, insulation fiber glass(Owens-Corning Fiberglass, Toledo, Ohio) having colorless fibers about 5μm in diameter and 300 to 700 μm in length. The mixture was sintered inair in a muffle furnace and allowed to cool to room temperature, formingthe advanced composition filtration media.

The advanced composite filtration media of this example had apermeability of 0.09 Da, a wet density of 16.0 pounds per cubic foot(i.e., 0.256 g/cm³), and 0.1% cristobalite.

The product is unique in that the microstructural features of thefiberglass are retained. Thus, the advanced composite filtration mediaof this example offers highly unique properties not offered by theindividual media components.

Example 8

Diatomite (80%)+Tin (20%)

In this example, an advanced composite filtration media was formulatedby combining 80% by weight of a functional filtration component, CELITE500, a natural diatomite with a permeability of 0.06 Da, a wet densityof 17.0 pounds per cubic foot (i.e., 0.272 g/cm³), and a median particlediameter, D₅₀ (a), of 16.7 μm (Celite Corporation, Lompoc, Calif.), and20% by weight with a matrix component, tin powder (Johnson-Matthey, WardHill, Mass.) of less than 100 mesh and of 99.5% purity. The mixture wassintered in air in a muffle furnace at 220° C. for 30 min, then removedfrom the furnace and allowed to cool to room temperature, forming theadvanced composite filtration media.

The advanced composite filtration media of this example had apermeability of 0.06 Da, a wet density of 20.8 pounds per cubic foot(i.e., 0.333 g/cm³), and 0.3% cristobalite.

The product is unique in that microstructural analysis reveals smallopaque particles, spherical, ellipsoidal, or angular in shape, with ametallic sheen, such that features of tine are retained. Thus, theadvanced composite filtration media of this example offers highly uniqueproperties not offered by the individual media components.

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We claim:
 1. An advanced composite filtration media comprisingheterogeneous media particles, each of said media particlescomprising:(i) a diatomite component; and, (ii) an expanded perlitecomponent; wherein said diatomite component is intimately and directlybound to said perlite component.
 2. The advanced composite filtrationmedia of claim 1,wherein the permeability of said media is greater thanthe permeability of a simple mixture of said diatomite component andsaid perlite component; wherein the proportions of said diatomitecomponent and said perlite component in said simple mixture areidentical to those used in the preparation of said media.
 3. Theadvanced composite filtration media of claim 1,wherein the permeabilityof said media is greater than the permeability of a simple mixture ofsaid diatomite component and said perlite component by 5% or more;wherein the proportions of said diatomite component and said perlitecomponent in said simple mixture are identical to those used in thepreparation of said media.
 4. The advanced composite filtration media ofclaim 1,wherein the median particle diameter of said media is greaterthan the weighted average of:the median particle diameter of saiddiatomite component; and, the median particle diameter of said perlitecomponent; wherein the proportions of said diatomite component and saidperlite component are identical to those used in the preparation of saidmedia.
 5. The advanced composite filtration media of claim 1,wherein themedian particle diameter of said media is greater than the weightedaverage of:the median particle diameter of said diatomite component;and, the median particle diameter of said perlite component by 5% ormore; wherein the proportions of said diatomite component and saidperlite component are identical to those used in the preparation of saidmedia.
 6. The advanced composite filtration media of claim 1, furthercharacterized by a cristobalite content of 3% or less by weight.
 7. Theadvanced composite filtration media of claim 1, further characterized bya cristobalite content of 1% or less by weight.
 8. A compositioncomprising an advanced composite filtration media according to claim 1.9. The composition of claim 8, wherein said composition is in the formof a powder.
 10. The composition of claim 8, wherein said composition isin the form of a sheet, pad, or cartridge.
 11. The composition of claim8, wherein said composition is in the form of a monolithic support or anaggregate support.
 12. The composition of claim 8, wherein saidcomposition is in the form of a monolithic substrate or an aggregatesubstrate.
 13. A method of filtration comprising the step of passing afluid containing suspended particulates through a filter aid materialsupported on a septum, wherein said filter aid material comprises anadvanced composite filtration media according to claim
 1. 14. Theadvanced composite filtration media of claim 1 wherein said diatomitecomponent is thermally sintered to said expanded perlite component. 15.An advanced composite filtration media comprising heterogeneous mediaparticles, each of said media particles comprising:(i) a diatomitecomponent; and, (ii) a thermoplastic or thermoset polymer exhibitingthermoplastic behavior component; wherein said diatomite component isintimately and directly bound to said thermoplastic or thermoset polymercomponent.
 16. The advanced composite filtration media of claim15,wherein the permeability of said media is greater than thepermeability of a simple mixture of said diatomite component and saidthermoplastic or thermoset polymer component; wherein the proportions ofsaid diatomite component and said thermoplastic or thermoset polymercomponent in said simple mixture are identical to those used in thepreparation of said media.
 17. The advanced composite filtration mediaof claim 15,wherein the permeability of said media is greater than thepermeability of a simple mixture of said diatomite component and saidthermoplastic or thermoset polymer component by 5% or more; wherein theproportions of said diatomite component and said thermoplastic orthermoset polymer component in said simple mixture are identical tothose used in the preparation of said media.
 18. The advanced compositefiltration media of claim 15,wherein the median particle diameter ofsaid media is greater than the weighted average of:the median particlediameter of said diatomite component; and, the median particle diameterof said thermoplastic or thermoset polymer component; wherein theproportions of said diatomite component and said thermoplastic orthermoset polymer component are identical to those used in thepreparation of said media.
 19. The advanced composite filtration mediaof claim 15,wherein the median particle diameter of said media isgreater than the weighted average of:the median particle diameter ofsaid diatomite component; and, the median particle diameter of saidthermoplastic or thermoset polymer component by 5% or more; wherein theproportions of said diatomite component and said thermoplastic orthermoset polymer component are identical to those used in thepreparation of said media.
 20. The advanced composite filtration mediaof claim 15, further characterized by a cristobalite content of 3% orless by weight.
 21. The advanced composite filtration media of claim 15,further characterized by a cristobalite content of 1% or less by weight.22. A composition comprising an advanced composite filtration mediaaccording to claim
 15. 23. The composition of claim 22, wherein saidcomposition is in the form of a powder.
 24. The composition of claim 22,wherein said composition is in the form of a sheet, pad, or cartridge.25. The composition of claim 22, wherein said composition is in the formof a monolithic support or an aggregate support.
 26. The composition ofclaim 22, wherein said composition is in the form of a monolithicsubstrate or an aggregate substrate.
 27. A method of filtrationcomprising the step of passing a fluid containing suspended particulatesthrough a filter aid material supported on a septum, wherein said filteraid material comprises an advanced composite filtration media accordingto claim
 15. 28. The advanced composite filtration media of claim 15wherein said diatomite component is thermally sintered to saidthermoplastic or thermoset polymer component.
 29. An advanced compositefiltration media comprising heterogeneous media particles, each of saidmedia particles comprising:(i) a diatomite component; and, (ii) a fiberglass component; wherein said diatomite component is intimately anddirectly bound to said fiber glass component.
 30. The advanced compositefiltration media of claim 29,wherein the permeability of said media isgreater than the permeability of a simple mixture of said diatomitecomponent and said fiber glass component; wherein the proportions ofsaid diatomite component and said fiber glass component in said simplemixture are identical to those used in the preparation of said media.31. The advanced composite filtration media of claim 29,wherein thepermeability of said media is greater than the permeability of a simplemixture of said diatomite component and said fiber glass component by 5%or more; wherein the proportions of said diatomite component and saidfiber glass component in said simple mixture are identical to those usedin the preparation of said media.
 32. The advanced composite filtrationmedia of claim 29,wherein the median particle diameter of said media isgreater than the weighted average of:the median particle diameter ofsaid diatomite component; and, the median particle diameter of saidfiber glass component; wherein the proportions of said diatomitecomponent and said fiber glass component are identical to those used inthe preparation of said media.
 33. The advanced composite filtrationmedia of claim 29,wherein the median particle diameter of said media isgreater than the weighted average of:the median particle diameter ofsaid diatomite component; and, the median particle diameter of saidfiber glass component by 5% or more; wherein the proportions of saiddiatomite component and said perlite component are identical to thoseused in the preparation of said media.
 34. The advanced compositefiltration media of claim 29, further characterized by a cristobalitecontent of 3% or less by weight.
 35. The advanced composite filtrationmedia of claim 29, further characterized by a cristobalite content of 1%or less by weight.
 36. A composition comprising an advanced compositefiltration media according to claim
 29. 37. The composition of claim 36,wherein said composition is in the form of a powder.
 38. The compositionof claim 36, wherein said composition is in the form of a sheet, pad, orcartridge.
 39. The composition of claim 36, wherein said composition isin the form of a monolithic support or an aggregate support.
 40. Thecomposition of claim 36, wherein said composition is in the form of amonolithic substrate or an aggregate substrate.
 41. A method offiltration comprising the step of passing a fluid containing suspendedparticulates through a filter aid material supported on a septum,wherein said filter aid material comprises an advanced compositefiltration media according to claim
 29. 42. The advanced compositefiltration media of claim 29 wherein said diatomite component isthermally sintered to said fiber glass container.
 43. An advancedcomposite filtration media comprising heterogeneous media particles,each of said media particles comprising:(i) a functional filtrationcomponent selected from the group consisting of diatomite, expandedperlite, pumice, obsidian, pitchstone, and volcanic ash; and, (ii) amatrix component; wherein said matrix component has a softening pointtemperature less than the softening point temperature of said functionalfiltration component; and, wherein said functional filtration componentis intimately and directly bound to said matrix component.
 44. Theadvanced composite filtration media of claim 43, wherein said functionalfiltration component is selected from the group consisting of diatomite,expanded perlite, and volcanic ash.
 45. The advanced compositefiltration media of claim 43, wherein said functional filtrationcomponent is diatomite.
 46. The advanced composite filtration media ofclaim 43 wherein said functional filtration component is thermallysintered to said matrix component.
 47. An advanced composite filtrationmedia comprising heterogeneous media particles, each of said mediaparticles comprising:(i) a functional filtration component; and (ii) anatural glass; wherein said natural glass has a softening pointtemperature less than the softening point temperature of said functionalfiltration component; and, wherein said functional filtration componentis intimately and directly bound to said natural glass.
 48. The advancedcomposite filtration media of claim 47 wherein said functionalfiltration component is thermally sintered to said natural glass.
 49. Anadvanced composite filtration media comprising heterogeneous mediaparticles, each of said media particles comprising:(i) a functionalfiltration component; and (ii) expanded perlite, pumice, obsidian,pitchstone, or volcanic ash; wherein said perlite, pumice, obsidian,pitchstone, or volcanic ash has a softening point temperature less thanthe softening point temperature of said functional filtration component;and, wherein said functional filtration component is intimately anddirectly bound to said perlite, pumice, obsidian, pitchstone, orvolcanic ash.
 50. The advanced composite filtration media of claim 49wherein said functional filtration component is thermally sintered tosaid expanded perlite, pumice, obsidian, pitchstone or volcanic ash. 51.An advanced composite filtration media comprising heterogeneous mediaparticles, each of said media particles comprising:(i) a functionalfiltration component; and (ii) expanded perlite; wherein said perlitehas a softening point temperature less than the softening pointtemperature of said functional filtration component; and, wherein saidfunctional filtration component is intimately and directly bound to saidperlite.
 52. The advanced composite filtration media of claim 51 whereinsaid functional filtration component is thermally sintered to saidexpanded perlite.
 53. An advanced composite filtration media comprisingheterogeneous media particles, each of said media particlescomprising:(i) a functional filtration component; and (ii) fluxedexpanded perlite; wherein said fluxed expanded perlite has a softeningpoint temperature less than the softening point temperature of saidfunctional filtration component; and, wherein said functional filtrationcomponent is intimately and directly bound to said fluxed perlite. 54.The advanced composite filtration media of claim 53 wherein saidfunctional filtration component is thermally sintered to said fluxedperlite.
 55. An advanced composite filtration media comprisingheterogeneous media particles, each of said media particlescomprising:(I) a functional filtration component selected from the groupconsisting of diatomite, expanded perlite, pumice, obsidian, pitchstone,and volcanic ash; and (ii) a metal or metal alloy; wherein said metal ormetal alloy has a softening point temperature less than the softeningpoint temperature of said functional filtration component; and, whereinsaid functional filtration component is intimately and directly groundto said metal or metal alloy.
 56. The advanced composite filtrationmedia of claim 55 wherein said functional filtration component isthermally sintered to said metal or metal alloy.